This invention relates to a circuit arrangement for operating at least a discharge lamp by means of a direct voltage source. The circuit arrangement is provided with:
direct voltage input terminals for connection of the direct voltage source, PA1 alternating voltage output terminals for connection of the discharge lamp, PA1 a direct voltage/alternating voltage converter and PA1 a current limiter for limiting the current through the lamp in the operating condition.
A circuit arrangement of the king mentioned in the opening paragraph is know from German Patent Specification No. 1,149,111. This arrangement is suitable for operating low-pressure discharge lamps in transport means. It is usual that lamps thus operated are operated at high frequency. The term "high frequency" is to be understood herein to mean a frequency of 500 Hz or higher.
Low-pressure discharge lamps are particularly suitable for illumination of the interior of a transport means and are frequently used for this purpose. However, they are not particularly suitable for use as a headlight due to their comparatively large dimensions. However, high-pressure discharge lamps are suitable for use as headlights and they have been proposed as such in the literature.
However, it is objectionable to operate a high-pressure discharge lamp with the known circuit arrangement because in the known circuit arrangement the direct voltage/alternating voltage converter supplies a rectangular alternating voltage. This may give rise to an unstable operation of the lamp due to acoustic resonances.
This disadvantage can be obviated by using a known converter which supplies a sinusoidal output voltage.
Another disadvantage of the known arrangement is that power regulation is not possible. However, in general a high-pressure discharge lamp exhibits, after starting, a transient phase before a stable operating condition is reached. During the said transient phase, a stable arc discharge is developed in the lamp after breakdown during starting, which is associated with a gradual rise of the voltage across the lamp. The transient behaviour of the lamp can be influenced by influencing the current through the lamp and hence the power dissipated in the lamp,